1. Field of the Invention
This invention relates to piston rings employed in pistons of internal combustion engines, and more particularly to design enhancements of oil control piston rings employed in such pistons.
2. Description of the Prior Art
Those skilled in the art will appreciate that the pistons of internal combustion engines in today""s modern vehicles are generally provided with three sets of piston rings for minimizing, between the pistons and their associated cylinder bores, the leakage of combustion gases to the engine crankcase, or of oil vapors to the combustion chamber.
A compression ring is generally provided in an upper region of a piston and is one hundred percent dedicated to operate as a gas-sealing medium, so as to prevent entry of combustion gases into the engine crankcase. A so-called lower compression ring is generally provided in a medial region of the piston body, providing approximately forty percent of the noted gas sealing function and sixty percent of an oil scrapping function. The lower compression ring is generally effective to prevent oil vapors from traveling up to the top of the piston head to create the classic smoking tailpipe or xe2x80x9cblue smokexe2x80x9d syndrome.
Finally, most modern pistons include a third piston ring called a lower or xe2x80x9cbottomxe2x80x9d oil control ring designed one hundred percent for aggressive scrapping of oil, and that is particularly adapted to force the oil back into the crankcase. Normally the oil control ring is the bottom-most piston ring, and in many modern engines constitutes a U-shaped flexible multidimensional ring. Accordingly, the ring includes a medial web supporting two spaced rail portions integrally connected to the web.
It will thus be appreciated that various piston rings are designed to address either or both of the noted functions of prevention of leakage of gas to the crankcase, or of oil to the piston head. Generally, as the rings wear during their continuous scrapping against the cylinder walls and associated rocking within piston ring grooves, issues of blow-by of gases into the crankcase, and oil leakage into combustion chamber areas, become significant. Most rings incorporate an initial tangential tension in their structures (as measured by a spring band) against the cylinder walls. This initial force, however, tends to diminish during the useful life of the piston ring.
Although substantially improved over the past decade, piston rings of modern engines remain deficient in various other respects as well. For example, in spite of the valuable scrapper function performed by the bottom oil control ring, an improved oil ring compression control against the cylinder walls during the engine break-in period for enhancing performance during said period would be quite desirable.
The present invention provides a mechanism for optimizing radial pressure of a piston oil control ring against the cylinder wall of a cylinder bore during the break-in period of an engine. An oil control ring for a piston of an internal combustion engine has an annular body defining a central axis. The ring has a U-shaped cross-section formed of a centrally positioned web extending parallel to the axis, and a pair of axially spaced rail portions integrally connected to the web. Each rail portion extends radially outwardly with respect to the web, and an extremity of each rail portion defines a land extending parallel to the axis and adapted to sealingly engage a cylinder wall.
Each land defines a pair of spaced concave annular sidewalls. Each sidewall extends contiguously from each land. The concave surface of each sidewall results in a reduction of land surface area in contact with the cylinder walls of an engine at any point during the engine break-in period. An improved performance, particularly during the engine break-in period, is realized through lower oil consumption and increased fuel economy.